The invention concerns a locking mechanism for safety belt retractors responding to movements and/or accelerations of the vehicle, with an annular inertia body held freely movable by means of an annular support secured on the housing and with a pivotally mounted pawl moved by the inertia body and arranged next to the latter for releasing and/or locking safety elements, e.g. the ratchet with a belt roller, inflating an air cushion, extending a head rest.
Such locking mechanisms with inertia-dependent sensors are already known, e.g. from U.S. Pat. No. 3,901,461 or German application No. 27 31 072. There the inertia body is a ball which is held freely movable in a trough and whose surface is in contact with a lug, likewise having a trough, on a pawl. In an accident, when a force is exerted on the vehicle and thus also on the belt roller, the ball moves relative to the trough, forcing the pawl into engagement with the ratchet wheel. The known support is designed as a ring, so that the uncertainty zone of the engagement between pawl and ratchet wheel can be kept small. It is also possible to effect the locking in a relatively short time by this type of support in the known locking mechanism and also the return of the inertia ball into its neutral position.
But in all known mechanisms of this type, the upper end of the movable inertia body describes a rather slow arc before the engagement takes place. This results necessarily in a considerable relative movement between the pawl, on the one hand, and the inertia body arranged as a rule under it, on the other hand. It is thus readily understandable that the factors influencing the response of the locking mechanisms, in other words, the sensitivity of the locking mechanism, is variable, and that the friction of the parts moving relative to each other is not always constant.
Particularly belt rollers for safety belts are, as known, mass-produced articles where minor deviations from the tolerances occur and are also permissible. It can readily happen that one inertia body has a slightly rougher surface than the other; and the same holds true for the friction surface of the pawl. These minor deviations increase their effect, however, e.g. when the friction surfaces are contaminated with dust, water, frozen condensed water, or a thin oil film.
It would be desirable to improve the locking mechanism of the above-described device whose mode of operation and function depend less on friction, and whose sensitivity and the corresponding response can therefore be more easily controlled.